Browsing by Keyword "silicon carbide"
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Item Discontinuous modulation of modular multilevel converters without the need for extra submodules(Institute of Electrical and Electronics Engineers Inc., 2015) Picas, R.; Ceballos, S.; Pou, J.; Zaragoza, J.; Konstantinou, G.; Agelidis, V. G.; Balcells, J.; POWER ELECTRONICS AND SYSTEM EQUIPMENTIn this paper, a new approach to the discontinuous modulation technique for the operation of the modular multilevel converter (MMC) is presented. Discontinuous modulation is based on adding a zero-sequence to the original modulation signals so that each MMC arm is clamped to the upper or lower terminals of the dc-link bus during some intervals. In combination with a circulating current control, the original discontinuous modulation can reduce the capacitor voltage ripple amplitudes and the switching power losses. However, additional submodules (SMs) are required to control the circulating current. This new approach presents a clamping algorithm that eliminates the requirement of additional SMs. As a result, the conduction losses are reduced while the capacitor voltage ripples are maintained low. Simulation and experimental results on a silicon-carbide-based MMC are reported and compared against the original discontinuous modulation and a conventional carrier-based pulse-width modulation.Item Thermally sprayed SiC coatings for offshore wind turbine bearing applications(2013-12) Mubarok, F.; Armada, S.; Fagoaga, I.; Espallargas, N.; EXTREMATTribological tests were conducted on thermally sprayed silicon carbide (SiC) coatings to investigate its potential on reducing wear in offshore wind turbine bearings. The tests were carried out under dry conditions, 3.5 wt.% NaCl solution, and polyalfaolefin (PAO)-lubricated conditions. In order to obtain good quality SiC coatings, it is compulsory to modify the feedstock to limit SiC decomposition during atmospheric spraying process. The SiC feedstock used in this research has been modified with yttrium aluminum garnet (Y 3Al5O12) oxide additives that originated from its metal salt precursors. High-frequency pulse detonation (HFPD) technique has been utilized to produce coatings of around 100 μm in thickness. The sliding tests have recorded the lowest coefficient of friction (COF) of 0.15 in PAO condition and the highest COF of 0.50 in dry sliding. The wear tracks morphology show that during dry sliding test, the coatings experience abrasive wear accompanied by tribo-oxidation reaction that initiates crack formation along the splat boundaries. On the other two sliding test conditions (NaCl and PAO), polishing of asperities and some grain plowing from the splats were observed in the wear tracks. Tribochemical wear was found to be the main mechanism producing smooth surfaces. Nevertheless, in all cases, the wear losses were negligible.